To modify a file, you should save it on your machine by
right-clicking the mouse on "Save File" hyperlink then choose
"Save target as ... " from the list, then you can edit the file using
a dedicated program installed on your machine.
Click "Browse .. " then choose the file you want to upload.
If you do not see a "Browse" button,
your browser does not support uploading.
Press "Upload File" and wait until the file is uploaded completely.
A message of "Uploading Succeeded" will appear when this step completes.
Depending upon both file size and your internet connection,
this operation needs time between 30 seconds and 15 minutes.
Press "Finish" to go back to properties page.